Red plum, red Roma and red round tomatoes were initially suspected as the cause of the salmonella outbreak though investigators are now widening their investigation. (Shari Vialpando/Associated Press)

With a salmonella scare causing many customers to shun what's normally a summertime favourite, tomato farmers across the United States have had to plow under their fields and leave their crop to rot in packing houses.

As losses across the supply chain top $100 million, industry leaders are calling for a U.S. congressional investigation into the government's handling of the outbreak, the source of which hasn't been determined.

On Thursday, Canadian officials confirmed that an individual who recently travelled to the U.S. has the same strain of salmonella identified in the American outbreak. A total of 922 cases have been confirmed in the U.S. The same strain of salmonella is also suspected to have been a contributing factor in the death of a Texas man.

"Now the government has a doubt as to whether it was tomatoes after they've already blackened our eye?" said Paul DiMare, president of the DiMare Cos. in Johns Island, S.C.

"June and July are the best time of the year for tomatoes, but our movement has completely stopped in the United States."

Tomatoes left to rot in fields

Farmers, packers and shippers fear it could take months to rebuild the $1.3-billion market for fresh tomatoes. In Fresno County, Calif., one grower chose to lose $225,000 US by letting his tomatoes rot in the fields this weekend because he would have taken a bigger hit hiring crews to harvest them, said Ed Beckman, president of the statewide co-operative California Tomato Farmers.

Like others in the produce trade, DiMare is critical of the U.S. Food and Drug Administration's progress on the investigation.

Officials with the FDA and Centers for Disease Control and Prevention have said the sheer complexity of the outbreak and the industry's vast international supply chain have hampered efforts to find the sources of contamination.

In April, before the first victim fell ill, U.S. agriculture authorities visited Florida packing houses and tomato farms on a special mission to assess food safety conditions.

At a handful of stops near Immokalee — located in one of the domestic regions still considered a possible origin of the outbreak — they found "conditions and practices of concern," including the presence of domestic animals, problems with the water system and poor sanitation, agency officials said.

All facilities corrected the problems immediately and none were deemed "egregious," FDA spokesman Michael Herndon said. Still, officials can't rule out the possibility that the salmonella may be linked to one of those locations.

Red plum, red Roma and red round tomatoes harvested in the area during that period were later shipped out to market and have yet to be cleared of suspicion. But they also have not been directly tied to the outbreak.

Last week, the FDA suggested tomatoes picked weeks ago could have tainted packing sheds or warehouses that are only now sending their products to market. There's also the possibility that the source itself is still on the market or that a different kind of produce is making people sick.